Production of high purity cyclohexane



May 3, 1966 R. M. WALDBY ETAI..v

PRODUCTION OF HIGH PURITY CYCLOHEXANE Filed Aug. '7, 1963 FEED W. O. SCHELLEN BERG A TTOPNEKS United States Patent O 3,249,642 PRODUCTION OF HIGH PURITY CYCLOHEXANE Roy M. Waldby, John H. Engel, and Walter 0. Schellenberg, Sweeny, Tex., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Aug. 7, 1963, Ser. No. 300,500 2 Claims. (Cl. 260-666) This invention relates to the production of high purity cyclohexane. In one aspect the invention relates to the removal of impurities in'a natural cyclohexane-containing fraction.

It is known to reform a natural cyclohexane-containing fraction to produce methycyclopentane by the catalytic conversion of the natural cyclohexane to benzene and to methylcyclopentane. It has also been shown that the methylcyclopentane can be recovered from the reformation unit effluent and subjected to isomerization of the methylcyclopentane to cyclohexane. A suitable process for this reformation is disclosed in U.S. Patent No. 3,009,002 issued to Carl M. Kron, November 14, 1961.

Under reformation conditions, the natural cyclohexane is converted in a catalytic reforming zone together with and in the presence of a reformer zone feed stock, for example, low end point reforming feed stock or gasoline, to produce not 'only methylcyclopentane but also benzene. It has been found that by subjecting the cyclohexane to reforming conditions results in conversion of to 20 percent per pass of the cyclohexane to methylcyclopentane with the majority of the remainder being converted to benzene. Since the ultimate desired product is generally high purity cyclohexane which requires methlycyclopentane for its production by isomerization, it is usually necessary to remove the benzene from the reforming zone eluent by solvent extraction or the like and to then subject the raffinate phase, containing the methylcyclopentane, to fractionation conditions so as to remove the normal heptane and heavier therefrom. However, also contained within the reforming zone feed stock are isoheptanes, such as 2,2-dimethlypentane, 2,4-dimethylpentane and 2,2,3-trimethylbutane which are converted to other products in the reforming unit, this conversion being 30 to 80 percent per pass, Heretofore, it has been the practice to fractionate the solvent extraction zone effluent to remove as bottoms the heptanes and heavier as gasoline product with the cut -being made so that the isoheptanes aforementioned are removed in the bottoms. However, this results in a considerable fraction of the methylcyclopentane being lost with the bottoms instead of being taken out overhead from the fractionating unit and sent to the isomerization unit. It has now been found that by alteration of the fractionation zone conditions it is possible to remove the 2,2-dimethylpentane, the 2,4-dimethylpentane, and the 2,2,3-trimethylbutane overhead along with the methylcyclopentane and the bulk of the cyclohexane for subjection .to isomerization conditions. Ultimately, the aforementioned isoheptanes are recycled to extinction in the reforming unit by conversion to a-wide variety of products such as cyclohexane and benzene and the like which are readily separable in the fractionating unit and recovered as desired cyclohexane. By this method it is possible to increase the recovery of high purity cyclohexane and also reduce the loss of methylcyclophentane in the bottoms from the fractionating unit.

lt is an object of the invention -to provide a method for the reformation of a natural cyclohexane-containing fraction.

It is another object of the invention to provide a method for the removal of impurities from lthe natural cyclohexane-containing feed stock to an isomerization unit.

3,249,642 Patented May 3, 1966 ICC It is another object of the invention to provide a process for the isomerization of methylcyclopentane to cyclohexane.

It is another object of the invention to provide a method for the recovery of methylcyclopentane and dimethylpentanes from a reformate stream.

These and other objects of the invention will be readily apparent to those skilled in the art from the accompanying disclosure, drawing and appended claims.

The invention is best described by reference to the following drawing which is a diagrammatic representation of the flow of the natural cyclohexane-containing feed stock through a combination of a hydrogenation unit, an isomerization unit and a reforming unit.

Referring now to the drawing, a natural cyclohexanecontaining feed stock, also containing methylcyclopentane, normal hexane, isohexanes, pentane, isopentanes, 2,2-dimethylpentane, 2,4-dimethylpentane, 2,2,3-trimethylbutane, methylcyclopentane and other close boiling impurities is fed through cond-uit 2 as feed into a depentanizer 4 where the C5s and lighter are removed overhead through conduit 6. The bottoms are passed through conduit 8 to prefractionator 9; the overhead is passed through conduits 11 and 10 into a deisohexanizer 12 wherein the isohexanes are removed overhead through conduit 14. The deisohexanized bottoms are removed through conduit 16 and passed into a demethylcyclopentanizer 18 wherein a fraction rich in cyclohexane is removed as bottoms -through conduit 20 for passage to a reforming unit hereinafter described. The overhead, which contains a small amount of benzene which is detrimental to the isomerization catalyst, is passed through conduits 22 and 24 into a hydrogenation unit 26 wherein the benzene is converted to cyclohexane in the presence of hydrogen introduced through conduit 2S. Hydrogenation is preferably the conventional catalytic operation using nickel on kieselguhr catalyst (Z5-60 percent nickel) at 300-500 p.s.i.g. and 400-500 F., using a mol ratio of hydrogen to benzene of about 9 to l. The eilluent from Ithe hydrogenation unit, having had hydrogen removed therefrom for recycle, is passed through conduit 30 into fractionator 32 wherein the pentanes and lighter are removed overhead through conduit 34. The bottoms are first dehexanized in dehexanizer 40 by passage through conduits 36 and 38. The overhead comprising normal hexane and isohexanes from the .dehexanizer is passed through conduit 42 into deisohexanizer 44 wherein the isohexanes are removed overhead through conduit 46. The bottoms contain a fraction rich in normal hexane and are removed through conduit 48 as a product. The bottoms from the dehexanizer 40 are removed through conduit' 50 and contain essentially methylcyclopentane with smaller quantities of normal hexane. Within the isomerization unit 52 the methylcyclopentane is converted to cyclohexane under isomerization zone conditions and the normal hexane is converted to isohexanes. The catalyst may be any conventional isomerization catalyst for this system. A suitable catalyst is the conventional aluminum chloride (hydrochloric aeidfortified) hydrocarbon complex catalyst. The efiiuent from the isomerization unit is passed through conduit 54 to a demethylcycopentanizer wherein the cyclohexane is removed as product through conduit 58. The purity of this product is in the order of 97+ percent cyclohexane. The overhead, containing principally methylcyclopentane normal hexane and isohexanes, is removed through conduit 60 and passed into a deisohexanizer 62 wherein the bottoms, containing Vprincipally methlycyclo., pentane and normal hexane, is removed through conduit 64 and combined with the bottoms from the fractionator 32 for passage into dehexanizer 40. The overhead from the deisohexanizer 62 is principally isohexanes which 24 to produce additional cyclohexane.

components are charged to the deisohexanizer 12 by way of conduits 66 and 10.

The bottoms stream from the demethylcyclopentanizer 18 is removed through conduit 20 and contains principally cyclohexane and 2,2-dimethy1pentane and IZA-dimethylpentane. This stream is joined with prefractionator 9 bottoms stream in conduit 68, and the blend is passed into reforming unit 70 through conduit 69 wherein the cyclohexane is converted to methylcyclopentane and benzene. In addition, the 2,2-dimethylpentane, the 2,4-dimethylpentane and the trimethylbutane components are also converted into cyclohexane, benzene, and numerous other products. The reforming unit eiuent is passed through conduit 72 and contains hexane components which are principally'methylcyclopentane and benzene, along w-ith toluene and other gasolinecomponents. Within the deheXanizer 74 a benzene-containing fraction, along with methylcyclopentane and isoheptanes, is removed overhead through conduit 7S while a toluene-containing fraction is l removed as bottoms through conduit 76. The overhead is passed through conduit 7S into a benzene solvent extraction unit l80 wherein the benzene is removed in the extract phase through conduit 80' as product. Any suitable process such as the Udex solvent extraction unit can be used for this separation. A portion, if desired, of the benzenecontaiuing extract is removed through conduit 82 and passed back to the hydrogenation unit 26 through conduit The raffinate is removed through conduit 84 and passed into a deisoheptanizer 86 operated so as to remove overhead the 2,2- and 2,4-dimethylpentanes.

, Heretofore, it has ybeen the conventional practice to. operate this tower 85 so as to remove as bottoms the heptanes and heavier and to also remove in the bottoms the 2,2- and 2,4-dimethylpentanes as well as the trimethylbutanes. This results in the inclusion in the bottoms of methylcyclopentane and cyclohexane, which are more valuable chemical products than as heptanes, which are principally used as fuel. It has now been found possible to delete from the system the 2,2- and 2,4-dimethylpentanes impurities which are not Iremovable by fractionation 5 due to their extremely close boiling points to methylcyclopentane by continuously recycling the dimethylpentanes and trimethylbutane ultimately to the reforming unit Wherein'they are converted at about 50 percent conversion per pass (recycled to extinction) to materials which are Ireadily separable from the methylcyclopentane. By this method it is possible to remove these impurities and thus increase the amount of recoverable methylcyclopentane lby simply adjusting the conditions within the deisoheptanizer 86. It-,h'as been found that a top temperature in the range of 230 F. to 250 F. and abottom .temperature in the range of 280t0 3009 F., and a pressure in the range of 30 to 40 p.s.i.g. results in the recovery in the bottoms `88 of the normal Cqs, S-ethylpentane, S-methylhexane, 2-methylhexane, 2,3-dimethylpentane, 3,3-dimethylpentane, and other similar boiling materials which have a boiling range inthe range Lof about 187 to 209 F. By this fractionation operation, it is possible to remove overhead small quantities of benzene, substantially all the methylcyclopentane and cyclohexane and lsubstantially all of the 2,2-dimethylpentane, the 2,4-dimethylpentane and the 2,2,3-trimethylbutane. This overhead is removed through conduit 90 vand joins the isohexane-containing stream in conduit 66 for passage back into the deisohexanizer 12. The stream then passes through demethylcyclopentanizer 18 and by way of conduit 20 the cyclohexane and 2,2- and `2,4-dimethylpentane are recycled back to the reforming unit wherein the impurities are reformed to extinction as hereinbefore described.

In order to better describe the invention, the following flow sheet is provided. Thisfflow sheet demonstrates one embodiment of the invention wherein a natural cyclohexane-containing feed is passed through a combination hydrogenation, isomerization and reformation operation.

TABLE L BARRELs/DAY Stream No 2 e s 11 6s 66 COMPONENT Pentane and lighter Isohexanes Normal hexane Methyleyclopenta-ne 1400 Benigno Cyclohexane 2,2-drnethylpentane 2,4-dmethylpentane Toluene Other isoheptanes. Normal heptane+ Total 23, O3() 3, 200 19, 830 9,000

7, iso e, 000 6, 220

Stream N0 50 46 48 54 58 COMPONENT Ientane and lighter Isohexanes Normal hexane Methylcyclopentane. Benzene Cyclohexane 2,2-dimethylpentane- 2,4-dimethylpentane Tnlnem3 2, 500 Other isoheptanes 2, 600 Normal heptane+ 3, 890

Total 6, 180 1, 130 1, 100 6, 100 2, 140 3, 960 870 1, 670 1, 180 10, 300

TABLE IL OPERATING CONDITIONS Tower 4 12 18 32 i 40 44 56 62 86 74 9 Process 70 26 52 CONDITION CONDITION Top temp, F 160 235 230 275 225 225 235 220 240 275 240 Pres., p.s.i.g 400 375 160 BTM temp. F 3l0 270 270 34() 250 235 285 235 290 320 300 Temp., F 930 45() '145 BTM pres., p.s..g 55V 30 130 35 35 45 35 V 35 35 40 While certain examples, structures, compositions and process steps have been described for purposes of illustration, the invention is not limited to the-se. Variation and modification Within the scope of the disclosure `and the claims can readily be effected by those skilled in the art.

We claim:

1. A process yfor the production of high purity cyclohexane `from a natural cyclohexane-containing feed also containing normal hexane, methylcyclopentane, 2,2-dimethylpentane and ZA-din'rethylpentane which comprises recovering in a first fractionation zone a first fraction from said feed containing cyclohexane, recovering from said feed a second ffraction containing methylcyclopentane subjecting said second fraction to an isomerization condition to convert said methylcyclopentane to cyclohexane, recovering the resultant high purity cyclohexane, subjecting said first fraction to reformation conditions to convert said cyclohexane to methylcyclopentane and benzene, recovering a third fraction containing benzene from the reformation effluent leaving a fourth fraction containing methylcyclopentane, cyclohexane, 2,2-dimethylpentane and 2,4- dimethylpentane, higher boiling isomers of heptane and heavier, recover-ing a fifth fraction yby Vfractionation of said fourth fraction containing rnethylcyclopentane, cyclohexane, 2,2-dimethylpentane and 2,4-dimethylpentane and recycling said fifth fraction to said first fractionation Zone.

2. A process for the production of high purity cyclohexane from a natural cyclohexane-containing feed also containing normal hexane, isohexanes, methylcyclopentane, 2,2-dimethylpentane, 2,4-dimethylpentane, 2,2,3- trimethylbutane and benzene which comprises recovering by fractionation of said feed a first vfraction containing isohexanes and leaving a second fraction, recovering a third fraction containing cyclohexane by Afractionation of said second fraction leaving a fourth fraction containing methylcyclopentane, benzene and normal hexane, subjecting said fourth fraction to benzene hydrogenation conditions to convert said benzene to cyclohexane, recovering normal hexane and isohexanes from the hydrogenation efliuent leaving a fifth fraction containing methylcyclopentane, subjecting said iifthfraction to isomerization conditions to convert said zmethylcyclopentane to cyclohexane, recovering said cyciohexane `as high purity product, subjecting said third `fraction to reforming conditions to convert said cyclohexane to methylcyclopentane and benzene, recovering benzene `from the reformation zone eiiiuent and leaving a sixth fraction containing 2,2-dimethy1pentane, 2,4-dirnethylpentane, 2,2,3-trimethylbutane, methylcyclopentane, cyclohexane, higherboiling isomers of heptane and heavier, subjecting said sixth fraction to thermal fractionation to remove said higher boiling isomers of heptane and heavier as bottoms and a seventh fraction containing rnethylcyclopentanm cyclohexane, 2,2-dimethylpentane, 2,4-dimethylpentane, and 2,2,3-trirnethylbutane as overhead and combining said seventh fraction with said second fraction.

References Cited by the Examiner UNITED STATES PATENTS 2,999,890 9/1961 -Davison 260-666 3,009,002 11/ 1961 Kron 260-667 DELBERT E. GANTZ, Primary Examiner.

PAUL M. COUGHLAN, Primary Examiner.

V. OKEEFE, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF HIGH PURITY CYCLOHEXANE FROM A NATURAL CYCLOHEXANE-CONTAINING FEED ALSO CONTAINING NORMAL HEXANE, METHYLCYCLOPENTANE, 2,2-DIMETHYLPENTANE AND 2,4-DIMETHYLPENTANE WHICH COMPRISES RECOVERING IN A FIRST FRACTIONATION ZONE A FIRST FRACTION FROM SAID FEED CONTAINING CYCLOHEXANE, RECOVERING FROM SAID FEED A SECOND FRACTION CONTAINING METHYLCYCLOPENTANE SUBJECTING SAID SECOND FRACTION TO AN ISOMERIZATION CONDITION TO CONVERT SAID METHYLCYCLOPENTANE TO CYCLOHEXANE, RECOVERING THE RESULTANT HIGH PURITY CYCLOHEXANE, SUBJECTING SAID FIRST FRACTION TO REFORMATION CONDITIONS TO CONVERT SAID CYCLOHEXANE TO METHYLCYCLOPENTANE AND BENZENE, RECOVERING A THIRD FRACTION CONTAINING BENZENE FROM THE REFORMATION EFFLUENT LEAVING A FOURTH FRACTION CONTAINING METHYLCYCLOPENTANE, CYCLOHEXANE, 2,2-DIMETHYLPENTANE AND 2,4DIMETHYLPENTANE, HIGHER BOILING ISOMERS OF HEPTANE AND HEAVIER, RECOVERING A FIFTH FRACTION BY FRACTIONATION OF SAID FOURTH FRACTION CONTAINING METHYLCYCLOPENTANE, CYCLOHEXANE, 2,2-DIMETHYLPENTANE AND 2,4-DIMETHYLPENTANE AND RECYCLING SAID FIFTH FRACTION TO SAID FIRST FRACTIONATION ZONE. 